Disc drives are used for data storage in modern electronic products ranging from digital cameras to computer systems and networks. A typical disc drive includes a head-disc assembly (HDA) housing the mechanical portion of the drive, and a printed circuit board assembly (PCBA) attached to the head-disc assembly. The printed circuit board assembly controls operations of the head-disc assembly and provides a communication link between the head-disc assembly and a host device served by the disc drive.
Typically, the head-disc assembly has a disc with a recording surface rotated at a constant speed by a spindle motor assembly and an actuator assembly positionably controlled by a closed loop servo system. The actuator assembly supports a read/write head that writes data to and reads data from the recording surface. Disc drives using magneto resistive read/write heads typically use an inductive element, or writer, to write data to the information tracks and a magnetoresistive element, or reader, to read data from the information tracks during drive operations.
One type of data recorded to and read from the information tracks is servo data. Servo data, including a physical track identification portion (also referred to as a servo track number or physical track number), written to the recording surface define each specific physical track of a number of physical tracks written on the recording surface. A servo track writer is traditionally used in writing a predetermined number of servo tracks to each recording surface during the manufacturing process. The servo tracks are used by the closed loop servo system for controlling the position of the read/write head relative to the recording surface during disc drive operations.
High performance disc drives achieve areal bit densities in the range of several gigabits per square centimeter (Gbits/cm2). Higher recording densities can be achieved by increasing the number of bits per centimeter stored along each information track, and/or by increasing the number of tracks per centimeter written across each recording surface. Capacity increases gained through increasing the bits per centimeter stored on each track generally require improvements in the read/write channel electronics to enable data to be written to and subsequently read from the recording surface at a correspondingly higher frequency. Capacity increases gained by increasing the number of tracks per centimeter on each recording surface generally require improvements in servo control systems, which enable the read/write heads to be more precisely positioned relative to the information tracks.
Signal loss in the disc drive is directly proportional to the distance the read/write head is from the information tracks and the wavelength of the signal. As density increases through increased bits per centimeter along the information track, controlling a fly height of the read/write head relative to the information track becomes more demanding. The ability to control the fly height of the read/write head relative to the information track through the mechanical configuration of the disc drive can no longer be depended on to produce disc drives while maintaining high yields in the manufacturing process.
Therefore challenges remain and needs persist for means of measuring the fly height of the read/write head within an assembled disc drive, referred to as an “in-situ” operation, absent the external measurement equipment to provide a basis for fly height control of the read/write head in a disc drive. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.